Ch.11 Life History-ISCI 3103

Flashcard maker : Henry Smith
Life History
-a record of events relating to its growth, development, reproduction, & survival
-It’s like a story of a species (life history strategy)
Characteristics that define the life history of an organism:
-age & size @ sexual maturity
-amount & timing of reproduction
-survival & mortality rates
Individual is to Life History as…
-weather is to climate
-photograph is to video
-page is to book
*your personal history of survival & reproduction is not a good representation of a species’ life history..life history should be the average values for all members of your species
There will always be variation among individuals within a species in..
survival, age @ reproduction, mortality rates, etc.
Life History Strategy
the life history strategy of a species is the overall pattern in the average timing & nature of life history events.
-it is determined by the way the organism divides its time & energy between growth, reproduction, & survival
Sample Life History Strategies
-James Bond approach
-Ryan Gosling approach
-Charlie Sheen approach
\”James Bond\” approach
-r strategist live fast, die young & leave a good looking corpse & a lot of offspring
\”Ryan Gosling\” approach
-k-selected; grow old & gray with that one special someone, raising one perfectly nurtured offspring
\”Charlie Sheen\” approach
-r & k; no kids of your own, but you help a relative raise children while maintaining your freedom; want genes passed along
How & why have particular life history patterns evolved?
-the theoretical ideal: life histories are optimal (maximization of fitness)
-life history strategies are not necessarily perfectly adapted to maximize fitness @ all times, particularly when environmental conditions change
Phenotypic plasticity
-one genotype may produce a continuous range of phenotypes under different environmental conditions (i.e. differences in appearance are NOT due to genetic differences)
-environmental conditions is what plasticity is about, not genetic
-phenotypic plasticity may produce a continuous range of growth rates; or discrete types—morphs
Polyphenism
-a single genotype produces several distinct morphs
-winged,non-winged ants
-carnivore or omnivore
-metamorph (leaves the water) or paedomorph (keeps it gills & stays in water)
Allometry
-different body parts grow @ different rates, resulting in differences in shape or proportion
Life History Strategy Variation
-reproductive strategy
-Gamete size
-life cycle complexity
-reproductive interval
-stress response
-dispersal & diapause
-changes through Ontogeny
Reproductive Strategy (life history strategy variation)
-sexual: fertilization
-asexual: simple cell division or simply no fertilization
-both
What are the advantages/disadvantages to sexual &/or asexual reproduction?
-costs: asexual-no genetic variation; disease; predation: sexual- more time; disease
-benefits: asexual-quicker, simple less prone to errors: sexual- population growth; more variation
Gamete Size (life history strategy variation)
-isogamy-gametes of relatively equal size
-anisogamy- gametes of unequal size
Gamete Size Hypothesis
sperm=abundant; cheap to build
eggs=limited; expensive to build
*Females are the \”choosy\” sex because they have more invested in reproduction=fewer eggs, greater energy expenditure
1. eggs are expensive, sperm are cheap, females should be picky
2. there is a biological basis for males to be \”less discerning\” when it come to mating (i.e. sleazy)
How does the gamete size hypothesis apply to natural selection & evolution?
-males with the best traits (what constitutes \”best\” will vary) will reproduce more & pass those traits on
How has female choice shaped behavior (a.k.a. \”what have women done to men?\”)?
-larger body size, more aggression, more colorful
-sacrifice life to feed pregnant females
-steal mating opportunities from friends
-establish dominance hierarchies (wolf pack)
-act like females just to get close to them
-hang around \”sexier\” males to intercept females
-mate guarding
-infanticide (lions)
-vaginal plugs & scoopers
-low threshold for sexual arousal
In rare cases the female is not \”in charge\” of reproduction:
-monogamy- 1 male, 1 female
-polygyny (many ginnies)- 1 male, multiple females-most common
-polyandry (many andys)- 1 female, multiple males
**even after we’ve mated successfully, females of some species can choose which sperm to fertilize eggs without the many matings they have solicited.
Choosers often can’t ascertain the health of a potential mate’s genes by sight, so they often rely on secondary sexual characteristics that indicate health:
ex: color
-calling effort in amphibians
-dung beetle, the bigger the dung, the better
Life Cycle Complexity (Life history strategy variation)
-complex life cycles involve @ least 2 distinct stages that may have different habitats
-transition between stages may be abrupt
metamorphosis
-abrupt transition form from the larval to the juvenile stage
-about 80% of animal species undergo metamorphosis @ some time in their life cycle
*However, some species have lost the complex life cycle & have direct development–the go from fertilized egg to juvenile without passing through a larval stage
Amphibian metamorphosis represents one of the most dramatic life history transitions of any organism on Earth, which includes:
1. changes in the digestive system from herbivory to carnivory
2. respiratory system-gills to lungs
3. fish-like locomotion to tetrapod
Reproductive Interval (Life history strategy variation)
-semelparous species reproduce only once (ex. salmon, century plant)
-iteroparous species can reproduce multiple times
**Why would any species reproduce this way?
-it works; they cycle still continues
-it’s a successful strategy
Stress Response (Life history strategy variation)
-stress response- more important for plants (immobile)
-a classification scheme for plant life histories is based on stress & disturbance (grime)
stress
-any factor that reduces vegetative growth
disturbance
-any process that destroys plant biomass
4 habitat types possible:
-low stress, low disturbance: competitors, rainforests
-high stress, low disturbance: dominated by \”stress-tolerant\” plants;
-low stress, high disturbance- ruderal plants
-high stress, high disturbance-beach; not suitable for plant growth
high stress, low disturbance habitats-dominated by \”stress-tolerant\” plants: how do they tolerate stress?
-low palatability (taste) to herbivores
-slow rates of nutrient + water uptake
-phenotypic plasticity
*stress tolerators are commonly found in extreme climates: deserts, boreal forest
low stress, high disturbance areas are dominated by \”ruderal\” plants:
-adapted to frequent disturbance typically through short life spans, rapid reproduction, heavy investment in seed production as opposed to vegetative growth
-seeds usually adapted to withstand disturbance until conditions are once again suitable
-ruderal plants often exploit habitats after a disturbance has remove competitive plants…meaning that, if the disturbance wasn’t there the competitive plants would win the war for space
low stress, low disturbance is the desired situations for plants if they could \”choose\”..
-they choose via competition..whoever competes best wins
-these habitats are dominated by \”competitive plants\”
**How do they compete?
-shading
-needles vs. leaves
-allelopathy-release toxins through root systems
Competition for light is one of the primary factors structuring plant communities
allelopathy
Allelopathy
-chemical warfare among plants
*What type of distribution among individuals you’ve learned about should result from allelopathy? Uniform
The interaction between \”competitors\”, \”stress tolerators\” & \”ruderals\” (i.e. disturbance tolerators) is modeled by:
-Grime’s Triangle
comparing to the r-k continuum:
-ruderal plants are similar to r-selected species; stress-tolerant plants correspond to k-selected species
-competitive plants occupy the middle of the r & k continuum.
Life History Trade-offs:
-organisms allocate limited energy or resource to one structure of function at the expense of another
What kinds of basic tradeoffs can you see that plants & animals (including yourself) might make?
-roots vs. leaves
– reproduction vs. everything else
-growth vs. reproduction
*Trade-offs shape & constrain life history evolution
*Foraging vs. breeding vs. defense vs. habitat choice
*most common reproductive tradeoff is between the number of size of offspring
These tradeoffs between number & size of offspring occur both inter- & intraspecifically:
-in addition, these tradeoffs may affect characteristics of offspring that influence their survival & fitness
Lack clutch size:
-maximum # of offspring a parent can successfully raise to maturity
* clutch size is limited by the maximum # of offspring the parents can raise @ one time (how many can you care for before you compromise your fitness? do you have the time, energy, resources to care for more?)
Trade-offs between current & future reproduction:
-for an iteroparous organism, the earlier it reproduces, the more times it can reproduce over its lifetime
-but not all reproductive events are equally successful. often the # of offspring produced increases with size & age of the organism
If sexual maturity can be delayed, an organism can invest more energy in growth & survival, & my increase its lifetime reproductive output. Why could this be so?
-losing #s
-storing up energy/resources
*under what conditions should an organism allocate energy to growth rather than reproduction? environmental conditions, weather
-long life span, high adult survival rates, & increasing fecundity (how many offspring you can have) with body size.
-if rates of adult survival are low, future reproduction may never occur, so early reproduction rather than growth would be favored.
Senescence
-decline in fitness of an organism with age & physiological deterioration
-onset of senescence can set an upper age limit for reproduction
-semelparous species undergo very rapid senescence & death following reproduction.
Dispersal & diapause (Life history strategy variation)
-some adults &/or their offspring are well-suited for dispersal
*benefit of dispersing: variation
-dispersal can reduce competition among close relatives & allow colonization of new areas
-dispersal can allow escape from areas with diseases or high predation
Diapause
-state of suspended animation or dormancy- organisms can survive unfavorable conditions:
-many seeds can survive long dormancy periods
-many animals can also enter diapause
Changes through Ontogeny (Life history strategy variation)
-even in organisms without abrupt shifts between life stages, different sized & aged individuals may have very different ecological roles
-a size-or stage-specific ecological role has been called an ontogenetic niche by Werner & Gilliam (Salamander)

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